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From "Bryan Pendleton (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-3130) Reduce memory footprint of StoredRecordHeader
Date Mon, 15 Oct 2007 16:48:51 GMT

    [ https://issues.apache.org/jira/browse/DERBY-3130?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12534895
] 

Bryan Pendleton commented on DERBY-3130:
----------------------------------------

Could you educate us a bit more about the StoredRecordHeader? What is
the life cycle of a StoredRecordHeader? (when are they created and when
reclaimed?). I'm trying to understand why your benchmark has 136,814
instances of the StoredRecordHeader: is that because your test touched
that many records in a single transaction? Or because you touched that
many records during the entire benchmark? Or because there were 136.8 records
per page and you had 1,000 pages in memory? Or some other reason? Thanks!


> Reduce memory footprint of StoredRecordHeader
> ---------------------------------------------
>
>                 Key: DERBY-3130
>                 URL: https://issues.apache.org/jira/browse/DERBY-3130
>             Project: Derby
>          Issue Type: Improvement
>          Components: Store
>    Affects Versions: 10.4.0.0
>            Reporter: Knut Anders Hatlen
>            Priority: Minor
>         Attachments: SmallRecordsTest.java, srh.diff
>
>
> Derby's page cache often has a memory footprint that is much larger than pageSize*pageCacheSize.
One large contributor to the footprint is the array of StoredPageHeader objects in BasePage.
The memory consumed by these objects can be as large as, and sometimes even larger than, the
byte arrays containing the raw page data. (See for instance http://www.nabble.com/How-much-derby-need-memory--tf3307655.html.)
Reducing the size of the StoredPageHeader objects could therefore reduce Derby's memory footprint
significantly, especially if the page cache is large and contains many pages from tables with
small records or from indices.

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